This invention relates to a flame retardant and moldable copolycarbonates derived from dihydric aromatic compounds and dihydroxy benzene mono or di sulfonic acids in the alkali metal salt form.
It is known from U.S. Pat. No. 3,043,800 dated July 10, 1962 that copolycarbonates can be prepared from dihydric aromatic compounds and dihydroxy benzene sulfonic acids. However, these copolycarbonates are indicated to be only useful as coatings and are soluble in aqueous alkali.
It is also known from U.S. Pat. No. 3,978,024 that homo-polycarbonates can be rendered flame retardant by sulfonation of the polycarbonates followed by neutralization of the sulfonic acid groups with alkali metal hydroxides. However, these sulfonated polycarbonates are not as effective as the copolycarbonates of the present invention as is shown in the examples herein.